Chinalco Mining Corp International said its Toromocho copper project has started production.

The mining project, in central Peru, is expected to achieve full capacity in the third quarter of next year and will turn out 220,000 metric tons of refined copper per year, accounting for 18 percent of China's total copper resources, the statement said. Toromocho will also produce molybdenum and silver.

But unreliable power supplies will hit output and copper production for 2014 is likely to be lowered by 20 percent, according to the statement issued late on Wednesday.

Lei Lianhua, a copper mining industry analyst, said it is common for preliminary production to be affected by erratic energy supplies, since Peru's copper output depends largely on electricity and water resources.

"The production at the initial stage may be reduced, but will not have a negative impact on the long-term production of this project," he said.